By Template tester plugin do you mean the builtin template tester?
I'm not sure what you mean by "only seems to let me process the book title." Are you referring to the template tester available from the Metadata plugboard page? If so then you see "fake" information instead of actual book metadata because the current context isn't the book list.
I suggest you test the templates in the main library using the template tester. Select the books of interest, open the tester (I defined the shortcut Ctrl+Alt+T to do that), write/run your template, then check the output. Depending on the complexity of what you are doing you might want to set breakpoints to help test/debug the template.
When happy, either
- copy the template into the clipboard and paste it into the appropriate plugboard box, or
- close the template tester with the OK button, open the template tester in the appropriate plugboard box, then right-click and choose "Load template from template tester."